Both phone and online Guardian/ICM surveys reported the same gap - up from 4% two weeks ago.

Leave now enjoys a 53%-47% advantage, once “don’t knows” are stripped out of the results, according to the research conducted over the weekend.

Corbyn said today: "A Vote to Leave is a vote to put our NHS in jeopardy, in the hands of those who want to break it up to end it as a service free at the point of use."

"Nigel Farage and Boris Johnson are wolves in sheep’s clothing, using their fake concern for the NHS to mask their real agenda."

He added: "Does anyone really believe that those from the hard right of the Tories and UKIP would spend any extra funds on the NHS? They’ve already promised this money again and again, on farming subsidies, fixing potholes and tax breaks no doubt for their rich friends and to corporations."

The Labour leader's warning echoes a recent attack on Boris Johnson and Michael Gove by Sir John Mayor.

The former Conservative prime minister and 'Remain' supporter, has said Gove wants to privatise the NHS and Johnson wants to charge for it. "The NHS is about as safe with them as a pet hamster would be with a hungry python," he told the BBC.